The wireless portable Internet system for further supporting mobility of a subscriber station to the wireless data communication system based on fixed access points such as the wireless LAN has recently been developed.
The IEEE 802.16 standard has adopted the OFDMA for a communication method if physical layers.
The OFDMA, which is an OFDM-FDMA communication method precisely, uses a plurality of subcarriers as a plurality of subchannels, and the wireless portable Internet system transmits with the same modulation level and channel coding scheme as a single burst, differing from the OFDM-TDMA system which transmits data to a subscriber station for each time slot. For ease of description, the OFDM-FDMA will be referred to as an OFDMA system hereinafter in an exemplary embodiment of the present invention. The OFDMA system is resistant against the fading generated by multipaths, and supports high data rates.
FIG. 1 shows a single-carrier resource allocation scheme.
As shown, a base station transmits data only to a single mobile station in the same symbol interval in the downlink according to the single carrier method, in which the symbol interval can be represented as a time slot. The base station uses predetermined burst profiles (including combinations of modulation methods and coding schemes) to arrange the burst profiles in the order from the most robust burst profile to the least robust one, and transmits the arranged burst profiles. Therefore, the subscriber station receives the bursts up to its operational burst profile, and ignores subsequent bursts having less robust burst profiles, thus minimizing power consumption caused by not processing the subsequent bursts. The OFDM-TDMA scheme follows the above-described power saving process for the plural carriers.
However, the OFDMA applied to the wireless portable Internet system allows the data to be transmitted to a plurality of subscriber stations in the same symbol period, and hence, the subscriber station must receive undesired bursts even though the received bursts are less robust burst profiles than that of the operational burst profile.
An OFDM communication scheme of the conventional wireless portable Internet system will be described.
FIG. 2 shows a hierarchical diagram of the IEEE 820.16 wireless portable Internet system including a physical layer L10 and media access control (MAC) layers L21, L22, and L23.
The physical layer L10 performs a wireless communication function such as modulation/demodulation, coding/decoding, etc. as performed by a normal physical layer. According to the IEEE 802.16e, the wireless portable Internet system does not have function-specific MAC layers as a wired Internet system, but a single MAC layer in charge of different functions. The MAC layer includes a privacy sublayer L21, a MAC common part sublayer L22, and a service specific convergence sublayer L23.
The service specific convergence sublayer L23 performs payload header suppression and QoS mapping functions in consecutive data communication.
The MAC common part sublayer L22 is the core of the MAC layer which is in charge of system access, bandwidth allocation, connection establishment and maintenance, and QoS control. The privacy sublayer L21 performs functions of equipment authentication and security key exchange, and encryption. The device authentication is carried on by the privacy sublayer L21, and the user authentication by an upper layer of the MAC (not illustrated).
FIG. 3 shows a schematic of a connection structure between a base station and a subscriber station in the wireless portable Internet system. A connection is provided between the MAC layers of the subscriber station (SS) and the base station (BS.) The term “connection C1” as used herein does not refer to a physical connection but a logical connection that is defined as a mapping relationship between the MAC peers of the subscriber station SS and the base station BS for tragic transmission of one service flow.
Hence, the parameter/message as defined on the connection C1 refers to a function executed between the MAC peers. Actually, the parameter/message is processed into a frame, which is transferred through the physical layer and analyzed so as to enable the MAC layer to execute the function corresponding to the parameter/message.
The frames representing radio resources allocated by the OFDMA scheme include a downlink sub-frame and an uplink sub-frame.
FIG. 4 shows a frame diagram for resource allocation in a downlink of the conventional OFDMA system.
A downlink subframe includes a downlink DL) frame prefix, MAP information, and a plurality d bursts. In the frame diagram, the ordinate axis represents sub-channels comprising orthogonal frequencies while the abscissa axis represents the time-divided symbol axis. The downlink bursts form a 2-dimensional square with respect to the symbol and subchannel axes. The MAP information has common control information including burst profile information, such as modulation and channel coding information, and the offset information, such as subchannel offsets and symbol offsets of burst to be received by the subscriber station.
As to the DL Burst #N, the less the number of N becomes, the more robust burst it is. That is, DL Burst #3 is more robust than DL Burst #4 and less robust than DL Burst #2.
Regarding to resource allocation method shown in FIG. 4, since the resource is allocated as an additional 2-dimensional square format for each burst, it frequently occurs that the more robust bursts are allocated until a later time. For example, DL Burst #2 and DL Burst #3 are transmitted until the later time in the temporal manner compared to DL Burst #4 and DL Burst #5.
Therefore, even when the subscriber station knows what bursts to receive (e.g., DL Burst #2), the subscriber station must receive other bursts that have less robust burst profiles (e.g., DL Burst #3, DL Burst #4, and DL Burst #5) in order to receive the burst to which the subscriber belongs, thereby generating undesired power consumption.
Also, the receiver processes DL Burst #2 later than DL Burst #4, and therefore, DL Burst #2 and DL Burst #4 may be transmitted to the upper layer in the wrong order. The burst which reaches a temporally subsequent symbol interval has a delayed processing time, and a corresponding response is accordingly delayed.
Further, since the resource is divided into non-uniform squares in the prior art, it may be possible that all the resources are not allocated and some resources remain.
FIG. 5 shows a conventional method for processing downlink resources for power saving.
A pipeline delay for default processing (which is a minimum processing time for the DL-MAP) is inevitable because of features of the OFDMA physical layers, the fast Fourier transform (FFT) is only performed during the pipeline delay, and the subsequent stages including demapping and channel decoding are difficult to execute.
As to managing the power saving, the subscriber station is controlled to process desired bursts and turn off the receiver when subsequent bursts are provided, thereby saving the power.
A designated burst (D-burst) may be allocated at a later time in the conventional resource allocation method shown in FIG. 4. That is, the burst which is less robust than the designated burst may be allocated prior to or concurrently with the designated burst.
Therefore, unnecessary bursts are also received while the designated burst is decoded, which is inefficient in the viewpoint of power saving. That is, further power is consumed for a useless process since the subscriber station receives bursts which are less robust than the general operational burst profile.
In addition, a surplus resource may be generated since the resources are allocated in the 2-dimensional square format in the prior art, and overhead may be larger since information on each burst in the MAP has symbol offset information and subchannel offset information.